JPH0424445B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing pitch graphitized fibers.

The method of producing carbon fiber using pitch as a raw material is advantageous compared to polyacrylonitrile systems because the raw material is inexpensive and the carbonization yield is high.It also has a heat treatment process such as infusibility, carbonization, or graphitization after spinning. If the treatment time can be shortened, the price advantage over polyacrylonitrile systems can be further clarified.

Up to now, various catalysts or accelerators have been investigated to shorten the infusibility treatment time, and metal salts, ammonium salts, inorganic acids, halogens, etc. have been proposed. In terms of the physical properties of the fibers, satisfactory results have not yet been obtained. For example, Pituchi fiber is mixed with hydrochloric acid,
When infusibility treatment is performed after contact treatment with an inorganic acid such as sulfuric acid or nitric acid, some products exhibit an infusibilization promoting effect, but this has the disadvantage of reducing the physical properties of the final product, carbon fiber.

On the other hand, Pitch-based graphitized fibers are produced by heat-treating carbonized fibers at 2000 to 3000°C in an inert gas atmosphere. The carbonized fibers referred to here are those obtained by heat-treating infusible fibers obtained by treating pitch fibers in an oxidizing gas atmosphere at 800 to 1300°C in an inert gas atmosphere, and are substantially It is a fiber that does not contain oxygen. Carbonization of these infusible fibers is usually carried out at a rate of 800 to 1300 °C in an inert gas at a rate of about 1 to 30 °C/min.
It is carried out by raising the temperature to about ℃,
At this time, it is said that increasing the temperature increase rate causes a decrease in the strength of the fibers. However, this method requires high temperatures for a long period of time, which not only leads to a decrease in productivity but is also economically disadvantageous.

In other words, in the production process of Pitch-based graphitized fibers, shortening the time for infusibility, carbonization, and graphitization is an issue, and there is a need for a firing process that simultaneously shortens this time and improves the physical properties of the product. There is.

As a result of intensive research, the present inventors have found that pitch fibers obtained by melt spinning carbonaceous pitch contain NO ₂ of 0.1 to 0.1%.
Processed in an oxidizing gas atmosphere containing 50 vol% to produce infusible fibers containing 0.1 to 5.0 wt% nitrogen,
By raising the temperature of the infusible fiber at a rate of 40°C/min or more in an inert gas atmosphere and heat-treating it at 2000 to 3000°C, the time required for the firing process can be significantly shortened, and the Pitch type has excellent performance. It was discovered that graphitized fibers can be obtained.

In addition, the present inventors treated pitch fibers obtained by melt spinning carbonaceous pitch in an oxidizing gas atmosphere containing 0.1 to 50 vol% NO ₂ to reduce the nitrogen content to 0.1.
After forming infusible fibers containing ~5.0 wt%, the infusible fibers are treated at 450 to 600°C in an inert gas atmosphere to become pre-carbonized fibers that substantially contain oxygen, and the pre-carbonized fibers are inert. By increasing the temperature at a rate of 40°C/min or more in a gas atmosphere and heat-treating at 2000-3000°C, the time required for the firing process can be significantly shortened, and a pitch-based graphitized fiber with excellent performance can be obtained. This is what we found together.

The invention will be described in detail below.

The carbonaceous pitch used in the present invention includes various pitches such as coal-based pitch such as coal tar pitch and SRC, petroleum-based pitch such as ethylene tar pitch and decant oil pitch, or synthetic pitch, but petroleum-based pitch is particularly suitable. preferable.

The above pitch is modified, for example, treated with a hydrogen donor such as tetralin, 20-350 kg/
The present invention also covers various modified pitches, such as those hydrogenated under hydrogen pressure of ^cm2 , those modified by heat treatment, those modified by means such as solvent extraction, or those modified by an appropriate combination of these methods. This is carbonaceous pitch.

That is, the carbonaceous pitch of the present invention is used to collectively refer to precursor pitches capable of forming pitch fibers.

The carbonaceous pitch of the present invention may be an optically isotropic pitch or an optically anisotropic pitch.

When the pitch is optically isotropic, the reflectance is
Those exhibiting a value within the range of 9.0 to 11.0% are preferred.
Here, the reflectance is measured by embedding a pitch in a resin such as acrylic resin, polishing it, and measuring it in air using a reflectance measuring device.

Optically anisotropic pitch is an optically anisotropic phase obtained by heat-treating pitch, usually at 340 to 450°C, while passing an inert gas such as nitrogen under normal pressure or reduced pressure. It is particularly preferable to use a pitch containing an optical anisotropy of 5 to 100%.

The carbonaceous pitch used in the present invention has a softening point of 200~
A temperature of 400°C is preferred, and a temperature of 240 to 300°C is particularly preferred.

Pitch fibers can be obtained by melt spinning the carbonaceous pitch using a known method. for example,
Pitch fibers are obtained by melting carbonaceous pitch at a temperature 30 to 80° C. higher than its softening point, and drawing it at 100 to 2000 m/min while extruding it through a nozzle with a diameter of 0.1 to 0.5 mm.

Next, the pitch fiber is infusible in an oxidizing gas atmosphere containing 0.1 to 50 vol% _NO2 .
The NO ₂ concentration is preferably 1 to 10 vol%, more preferably 1 to 5 vol%.

The infusibility treatment time is 5 to 50 minutes, preferably 10 minutes.
~30 minutes. If the infusibility time is less than 5 minutes, the infusibility is insufficient, leading to fusion of the fibers in the subsequent process. On the other hand, if the infusibility time exceeds 50 minutes, it is not only industrially disadvantageous, but also may lead to a decrease in the physical properties of the graphitized fiber. The infusibility reaction is performed when the nitrogen content in the infusible fiber is 0.1~
The content is adjusted to 5.0wt%, preferably within the range of 0.2 to 4.0wt%. If the nitrogen content is out of the above range, the
The temperature cannot be raised effectively at a rate of ℃/min or more, and the physical properties of the graphitized fiber obtained deteriorate. Infusibility treatment is usually
The preferred treatment temperature is 400℃ or below.
The temperature is 150 to 380°C, more preferably 200 to 350°C. If the treatment temperature is too low, the treatment time becomes long, and if the treatment temperature is too high, phenomena such as fusion or consumption of the pitch fibers occur, which is not preferable. The heating rate is 1 to 100℃/min.
Preferably 2-50°C/min, more preferably 5-50°C
°C/min. As the oxidizing gas, one or more of oxidizing gases such as oxygen, ozone, air, sulfur oxide, or halogen are usually used. In the present invention, oxygen and air are particularly preferred.

If necessary, the infusible fibers can be treated at 450 to 600° C. in an inert gas atmosphere to become pre-carbonized fibers that substantially contain oxygen. The pre-carbonization treatment is carried out within the above temperature range, and the treatment time is not limited, but is usually 10 seconds to 1 hour, preferably 1 hour.
Minutes to 10 minutes. In addition, the temperature increase rate in pre-carbonization is 1°C/min to 2000°C/min, preferably 4°C/min to
1000℃/min.

Graphitized fibers can be obtained by heating the thus obtained infusible fibers or pre-carbonized fibers at a rate of 40° C./min or more and heat-treating them at 2000 to 3000° C. in an inert gas atmosphere. In the present invention, infusible fibers or pre-carbonized fibers containing substantially oxygen are heated to a predetermined temperature of 2,000 to 3,000°C at a rate of 40°C/min or more, and heat-treated for a predetermined period of time to produce high-strength pitch fibers. As a result, graphitized fibers can be obtained.
Even if so-called carbonized fibers that do not contain substantially oxygen are heat-treated at 2000 to 3000° C., the strength of the graphitized fibers obtained by the method of the present invention is not as high as that of the fibers obtained by the method of the present invention. The pre-carbonized fibers substantially containing oxygen herein are fibers containing 1 to 40% by weight, preferably 3 to 10% by weight of oxygen. The graphitization treatment time is 1 second to 1 hour, preferably 5 seconds to 10 minutes. The heating rate to the graphitization temperature is 40°C/min or more, preferably 100°C/min or more, more preferably
The temperature is 500°C/min or more, most preferably 1000°C/min or more.

If the temperature increase rate is less than 40° C./min, or if the infusible fibers are first converted into carbonized fibers and then the carbonized fibers are graphitized, graphitized fibers with excellent physical properties cannot be obtained.

EXAMPLES The present invention will be specifically explained below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

Example 1 Contains 80% optically anisotropic phase and has a softening point of 280°C
The petroleum precursor pitch was melt-spun to obtain pitch fibers with an average diameter of 13μ. This pitch fiber,
In an oxygen atmosphere containing 2 vol % of NO ₂ , the temperature was raised from 30°C to 270°C at a rate of 10°C/mm to perform infusibility treatment for 24 minutes.
The treated fibers contained 2.4 wt% nitrogen.
Then, the temperature was increased to 2500℃ at 100℃/mm, and at 2500℃
When graphitized for 10 seconds, the graphitized fibers obtained had an average thread diameter of 10 μ, an elastic modulus of 60 TON/mm ² and a tensile strength of 330 Kg/mm ² .

Comparative Example 1 The infusible fiber of Example 1 was heated in nitrogen at a rate of 10° C./mm and carbonized at 1000° C. for 30 minutes to produce carbon fiber. When the obtained carbon fibers were graphitized at 2500℃ for 10 seconds, the obtained graphitized fibers had an average yarn diameter of
10μ, elastic modulus 55TON/mm ² , tensile strength 270Kg/mm ²
It was hot.

Comparative Example 2 The pitch fiber of Example 1 was heated at 10°C/mm in oxygen.
The temperature was raised to 270℃ for infusibility treatment, and then heated to 100℃/
When the temperature was raised to 2500℃ in mm and graphitized at 2500℃ for 10 seconds, the graphitized fibers obtained had an average yarn diameter of
10 μ, elastic modulus 55 TON/mm ² , and tensile strength 220 Kg/mm ² .

A comparison between Example 1 and Comparative Examples 1 and 2 shows that the graphitized fiber produced by the method of the present invention has superior performance compared to the conventional method.

Example 2 Contains 65% optically anisotropic phase and has a softening point of 252°C
The petroleum precursor pitch was melt-spun to obtain pitch fibers with an average diameter of 11μ. This pitch fiber,
150℃ at 5℃/mm in air containing 5vol% NO ₂
The temperature was raised from 290°C to 290°C, and infusibility treatment was performed for 28 minutes. The treated fibers contained 0.3 wt% nitrogen. Then, it was treated at 500°C to produce a pre-carbon fiber. The obtained pre-carbon fiber contains 5% by weight of oxygen, which is heated to 2500°C at a rate of 1000°C/mm.
When graphitized at 2500° C. for 60 seconds, the graphitized fibers obtained had an average thread diameter of 9 μ, an elastic modulus of 70 TON/mm ² and a tensile strength of 320 Kg/mm ² .

Example 3 An optically isotropic petroleum precursor pitch with a reflectance of 10.3% and a softening point of 270°C was melt-spun, and the average yarn diameter was
A 12μ pitch fiber was obtained. This pitch fiber,
150℃ at 5℃/mm in air containing 2vol% NO ₂
The temperature was raised from 300°C to 300°C, and infusibility treatment was performed for 30 minutes. The treated fibers contained 0.8 wt% nitrogen. Pre-carbonized fibers were then processed at 500°C. The oxygen content of the obtained pre-carbonized fiber was 4.5% by weight. The carbonized fiber was heated to 2500℃ at 50℃/min.
The physical properties of the graphitized fiber obtained were an elastic modulus of 65 TON/mm ² and a tensile strength of 260.
It was Kg/ ^mm2 .

Example 4 The pitch fiber in Example 1 was heated in oxygen containing 5 vol % of NO ₂ at a rate of 5° C./mm from 130° C. to 280° C. and subjected to infusibility treatment for 30 minutes. The treated fibers contained 1.8 wt% nitrogen. It was then treated at 500°C to produce pre-carbonized fibers. The oxygen content of the obtained pre-carbonized fiber was 6.0% by weight. Before this, the carbonized fiber was heated to 2500°C at 3000°C/min, and then heated to 2500°C.
When treated for 30 seconds, the physical properties of the graphitized fiber obtained were an elastic modulus of 60 TON/mm ² and a tensile strength of 330 Kg/mm ² .

Example 5 The pre-carbonized fiber in Example 3 was heated at 500°C/min.
When the temperature was raised to 2000℃ and treated at 2000℃ for 1 minute, the elastic modulus was 40TON/mm ² and the tensile strength was 200Kg/mm ²
It was hot.

Comparative Example 3 Pitch fiber in Example 1 was mixed with 75vol of _NO2 .
% oxygen at 10℃/min from 30℃ to 270℃
The temperature was raised to ℃ and the infusibility treatment was performed for 24 minutes. The treated fibers contained 9 vol% nitrogen. Then
When the temperature was raised to 2500℃ at 100℃/min and graphitized at 2500℃ for 10 seconds, the graphitized fibers obtained had an average thread diameter of 10μ, an elastic modulus of 40ton/mm ² , and a tensile strength of 210Kg/mm ²
It was hot.

Comparative Example 4 The pitch fiber in Example 1 was treated with NO ₂
In an oxygen containing 0.05 vol%, the temperature was raised from 30°C to 270°C at 10°C/min for 24 minutes to make it infusible.
The treated fibers contained 0.1 vol% nitrogen.
Then, the temperature was increased to 2500℃ at 100℃/min, and then the temperature was increased to 2500℃.
When graphitized for 10 seconds ^at
It was Kg/ ^mm2 .

Comparative Example 5 The pitch fiber in Example 2 was treated with NO ₂
150℃~ at 5℃/min in air containing 0.05vol%
The temperature was raised to 290°C and infusibility treatment was performed for 28 minutes.
The treated fibers contained 0.05 wt% nitrogen. The infusible fibers were then treated at 500°C to produce pre-carbonized fibers. The obtained pre-carbonized fiber is 1000
When the temperature was raised to 2500℃ at a rate of ℃/min and graphitized at 2500℃ for 60 seconds, the graphitized fibers obtained had an average thread diameter.
It had an elastic modulus of 9μ, an elastic modulus of 41 ton/mm ² , and a tensile strength of 220 Kg/mm ² .

Comparative Example 6 Pitch fiber in Example 2 was mixed with 75vol of _NO2 .
% in air, the temperature was raised from 150°C to 290°C at 5°C/min, and the infusibility treatment was performed for 28 minutes. The treated fibers contained 8 wt% nitrogen. The infusible fibers were then treated at 500°C to produce pre-carbonized fibers. The obtained pre-carbonized fiber was heated at 1000℃/min.
When the temperature was raised to 2500°C and graphitized at 2500°C for 60 seconds, the graphitized fibers obtained had an average thread diameter of 9μ, an elastic modulus of 42ton/mm ² , and a tensile strength of 190Kg/mm ² .

Claims (1)

[Claims] 1 Pitch fibers obtained by melt spinning carbonaceous pitch are treated in an oxidizing gas atmosphere containing 0.1 to 50 vol% of NO ₂ to make them infusible to contain 0.1 to 5.0 wt% of nitrogen. The infusible fibers are heated at a rate of 40°C/min or more in an inert gas atmosphere to 2000 to 3000°C.
1. A method for producing pitch-based graphitized fiber, which is characterized by heat treatment. 2. The method according to claim 1, wherein the oxidizing gas is oxygen, ozone, air, sulfur oxide or halogen. 3 Pitch fibers obtained by melt-spinning carbonaceous pitch are treated in an oxidizing gas atmosphere containing 0.1 to 50 vol% NO ₂ to make infusible fibers containing 0.1 to 5.0 wt% nitrogen, and then 450~ under active gas atmosphere
The pre-carbonized fibers are treated at 600°C to substantially contain oxygen, and the pre-carbonized fibers are heated at 40°C under an inert gas atmosphere.
A method for producing pitch-based graphitized fibers, which comprises raising the temperature at a rate of at least ℃/min and heat-treating at 2000 to 3000℃. 4. The method according to claim 3, wherein the oxidizing gas is oxygen, ozone, air, sulfur oxide or halogen.